Sony's got a shitload of exclusives of thier own already. And they do a much better job of holding onto them than Microsoft (especially since most are first party).
They ain't touching Nintendo either with the motion thingy, it's too late into the game, an optional peripheral, expensive and unproven - why should a third party developer even bother?
Its only purpose so far seems to be one upping Nintendo from a tech standpoint, something PS3 and 360 had been doing from day one anyways.